In copending patent application Ser. No. 06/588,478, filed Mar. 12, 1984 by Ross H. Freeman and entitled "CONFIGURABLE LOGIC ARRAY" which is incorporated herein by reference, a structure is described which allows changing the configuration of a finished integrated circuit from time to time (even when the integrated circuit is installed in a system) to provide any one of a plurality of logical functions from the same integrated circuit. This is accomplished by providing a number of "configurable logical elements" (herein referred to as "configurable logic elements") each of which is capable of being configured to implement any one of a plurality of logic functions depending on the task which it is called upon to perform. By configurable logic element (CLE) is meant a combination of devices which are capable of being electrically interconnected by switches operated in response to control bits stored on the chip (or transmitted to the chip) to perform any one of a plurality of logical functions. The configurable logic element disclosed in application Ser. No. 06/588,478 may include all of the circuit elements necessary to provide one or more of the functions provided by, for example, an AND gate, flip-flop, inverter, NOR gate, exclusive OR gate, and combinations of these functions to form more complex functions. The particular function to be carried out by a configurable logic element is determined by control signals applied to the configurable logic element from control logic. Depending on the control signals, a configurable logic element can function as an AND gate, an OR gate, a NOR gate, a NAND gate, or an exclusive OR gate or any one of a number of other logic functions without change in physical structure. Structure is provided on chip to allow any one of a plurality of functions to be implemented by the configurable logic element. This is done by providing control logic to store and generate control signals which control the configuration of the configurable logic element.
In one embodiment, the control signals are stored and transmitted by control logic formed integrally with and as part of the integrated circuit chip containing the configurable logic elements. However, if desired, the control information can be stored and/or generated outside the integrated circuit and transmitted through pins to the configurable logic element.
In general, a given set of control signals in the form of control bits is transmitted from the control logic to a configurable logic element to control the configuration of that configurable logic element. The actual set of control bits provided to the configurable logic element on the integrated circuit chip depends on the function to be carried out by the configurable logic element on the chip.
In copending U.S. application Ser. No. 706,429,filed Feb. 27, 1985, on an invention of William S. Carter, a particularly versatile configurable logic element is described which includes a configurable combinational logic element, a configurable storage element and a configurable output select logic. The output signals of the configurable storage element serve as input signals to both the configurable combinational logic and the output select logic. This configurable logic element, however, is not well suited to easy communication with a microprocessor since, for example, if a data signal from a microprocessor is stored in the configurable storage element, the configurable storage element is then not available to receive other output signals from the configurable combinational logic element. Moreover, communication between an array of such configurable logic elements and a microprocessor would require use of the general interconnect structure of the configurable logic array, reducing the versatility of the array.